Waking Up Rosetta

by Paul Gilster on January 20, 2014

In the first post of 2014, I wrote about what the following year — 2015 — would bring, the New Horizons flyby of Pluto/Charon as well as the arrival of the Dawn spacecraft at Ceres, a fascinating object with a possible internal ocean. But let’s not forget about the European Space Agency’s Rosetta spacecraft, which is now nearing the end of a decade-long journey to comet 67P/Churyumov–Gerasimenko. The spacecraft is scheduled to awake from a two-year stretch in sleep mode today, with arrival at the comet’s core in November. The orbiter will operate there until the end of 2015.

We’ve had missions to comets before, many of them discussed in these pages, but none as ambitious as this one. Rosetta’s Philae lander will attempt a landing on the comet in November while the orbiter will continue tracking it as the comet is transformed by its approach to the Sun into an erupting, churning mass of ice and dust. With gravity about a thousand times less than that of Earth, this is a tricky object to land on, but the visual rewards should be great, according to Michael Combi (University of Michigan), a co-investigator on several instruments aboard the craft:

“On the lander, there’s a camera that can look straight down like you’re standing up and looking at the ground. Then there’s a panoramic camera that can look out and see a picture of the horizon. It’ll be fun to see what this landscape looks like. It’ll be like standing on a comet.”

Image: An artist’s interpretation of the Rosetta mission lander, named Philae, on the core of comet 67P/Churyumov-Gerasimenko. It’s expected to land in November. Credit: ESA / AOES Medialab.

Rosetta’s investigations will be numerous, and many bear directly on issues we routinely discuss here. We’ve been looking, for example, at Pekka Janhunen’s concept of an electric sail that would ride the solar wind — a stream of charged particles flowing outward from the Sun — to distant destinations in the Solar System, reaching perhaps 100 kilometers per second. Rosetta will be studying the interactions of the solar wind with cometary gases to learn more about the composition of the charged particles and help us better understand solar storms.

That’s the kind of space ‘weather’ an electric sail would confront as it makes its long journey to system’s edge. This University of Michigan news release notes that the solar wind travels more slowly from the area of the Sun’s equator, but moves much faster at higher latitudes. Comets pass through a wide range of solar wind conditions and thus offer an ideal way to study the phenomenon. Accurate control and navigation of future craft riding the solar wind will depend upon our understanding of its turbulent interactions.

Comets are also useful in teaching us about the origin and evolution of the Solar System, as they were present in the nebula from which the system grew and have been orbiting far from the Sun ever since. We still have much to learn about their role in delivering water to Earth’s oceans and possibly organic materials. Combi adds: “People use the analogy that it’s been in the freezer for the past 4.5 million years and brought in for convenient study. So we’re looking as much as we can at the way the way the solar system was 4.5 billion years ago.”

This recent NASA news release offers information about the three instruments the agency has contributed to the ESA mission:

An ultraviolet spectrometer called Alice, which analyzes the ultraviolet part of the spectrum, examining gases in the coma and tail to measure the water, carbon monoxide and carbon dioxide it finds there, along with other readings on the surface composition of the nucleus;

The Microwave Instrument for Rosetta Orbiter, combining a spectrometer and radiometer to read temperatures and identify chemicals on the comet’s surface and the dust and ices around it. This will be a key instrument in tracking changes as the comet approaches the Sun;

The Ion and Electron Sensor, used in characterizing the plasma environment of the comet and the interactions of the solar wind with the comet’s gases.

Image: An artist’s view of Rosetta, the European Space Agency’s cometary probe. The spacecraft is covered with dark thermal insulation in order to retain its warmth while venturing into the coldness of the outer solar system, beyond Mars orbit. Credit: ESA.

The European Space Agency’s Rosetta page is here, a place you’ll want to bookmark as the year progresses and Rosetta moves ever closer to its encounter with 67P/Churyumov–Gerasimenko. Thus far the spacecraft has made three Earth flybys and one flyby of Mars as it established its trajectory to the comet, with encounters with asteroids Steins and Lutetia along the way. Assuming all is going well, the spacecraft’s star trackers are now warming up, a six hour process, and adjustments will soon be made to its orientation to keep Rosetta’s solar arrays facing directly toward the Sun. Follow @ESA_Rosetta for confirmation that the wake-up procedure is complete, probably between 1730 and 1830 UTC. Keep an eye on this page for live video updates.

By the way, while this is a long time for a space probe to have been in hibernation and revived, this is not a record for a comet probe. Giotto was commanded to sleep in 1986 after its historic flyby of Comet Halley, then woken up in 1990 when it flew by Earth to flyby Comet Grigg-Skjellerup in 1992. Then it went back to sleep one month later but was not reawakened.

Speaking of long-lived comet probes, see this from Wikipedia about ICE, which was the first to flyby an ancient iceball in 1985:

“On September 18, 2008, NASA, with the help of KinetX, successfully located and reactivated ICE using the Deep Space Network. A status check revealed that all but one of its 13 experiments were still functioning, and it still has enough propellant for 150 m/s of ΔV. NASA scientists are considering reusing the probe to observe additional comets in 2017 or 2018.[5] Such a mission, however, would delay any attempt to capture the spacecraft until the 2040s. It is currently in a trajectory that will bring it close to Earth on August 2014.[6]”

Any plans on capturing it this August? I know, but I felt I had to ask out of principle.

A handsome prince, in the form of the European Space Agency (ESA), has planted a tender kiss on the lips of a sleeping princess, 418 million miles (673 million km) from the Sun. Yesterday it was triumphantly announced that the Rosetta spacecraft had been successfully reawakened after 31 months in deep-space hibernation and its decade-old mission is now back on track and closing in on an exciting conclusion: to orbit and land on the surface of Comet 67P/Churyumov-Gerasimenko.

The first signal from Rosetta was received by NASA’s 230 foot (70 meter) Deep Space Network (DSN) antenna at Goldstone, Calif., at 6:18 p.m. GMT (1:18 p.m. EST), during the first “window” of opportunity it had to contact Earth. The triumphant revival of the spacecraft prompted the European Space Operations Centre (ESOC) in Darmstadt, Germany, to tweet the message everyone had waited so long to hear: “Hello, world!”

Launched in March 2004, aboard a mighty Ariane 5 booster from the Guiana Space Centre in Kourou, French Guiana, Rosetta consists of an orbiter, laden with 12 scientific instruments, and the Philae landing craft, which carries 9 additional instruments. Named in honor of the Rosetta Stone—the discovery of which enabled Egyptologists to decipher ancient hieroglyphs—and the Nile island of Philae, whose obelisk helped to decipher the Stone, the mission is expected to decipher the history, composition, and evolution of a virtually untouched, primordial cometary object in unprecedented detail.

After departing Earth, Rosetta undertook a lengthy flight profile, whose convoluted trajectory carried it past the Home Planet on three separate occasions (in March 2005, November 2007, and November 2009), once past Mars (in February 2007) and past the asteroids Šteins in September 2008 and Lutetia in July 2010. Most recently, in June 2011, it was placed into a power-saving hibernation, and in that state it remained for 31 long months, as it drifted up to a maximum of 500 million miles (800 million km) from the Sun.

Its solar arrays were oriented in such a manner as to receive as much solar energy as possible and it was placed into a spin-stabilized mode. “Only the computer and several heaters” remained active, according to ESA at the time, “automatically controlled to ensure that the entire satellite doesn’t freeze.”

Rosetta’s lander — Philae — will actually fire a small harpoon into the surface of the comet to help anchor itself.

@Alex, keep in mind that this is a stable-ish short-term comet; it’s been in the same orbit for at least the last few decades. It currently orbits between about 1.2 to 5.5 AU… that is, from about halfway between Earth and Mars, out to just past the orbit of Jupiter. So we wouldn’t expect active chemistry in the sense of reactions happening — probably anything that was going to react, already has. But that doesn’t rule out all kinds of other interesting active processes happening on various time scales.

@ljk, ICE comes up periodically over at unmannedspaceflight.com. At this time there appear to be no plans for it.

I am looking forward to Rosetta’s mission. It should provide definitive evidence on which view of comets most closely matches up to reality:
the orthodox Dirty Snowball or
the very unorthodox Electric Comet

In the Dirty Snowball view comets are mostly ice and the heat from the sun sublimates the water away and causes the coma around the comet.

In the Electric Comet view, comets are made up of material more like asteroids then snowballs. And the coma that forms around the comet is caused electrical discharge between the comet and the plasma streaming from the sun. Not from the heat of the Sun.

Remember there is a disc on the lander with over 1,500 human languages on it set for very long-term preservation. Future linguists and historians may consider this one of the most valuable pieces of intellectual property in the Sol system, assuming nothing else like it is kept intact elsewhere over the centuries.

“So ISEE-3 will pass by us, ready to talk with us, but in the 30 years since it departed Earth we’ve lost the ability to speak its language. I wonder if ham radio operators will be able to pick up its carrier signal — it’s meaningless, I guess, but it feels like an honorable thing to do, a kind of salute to the venerable ship as it passes by.”

Hey ICE/ISEE-3, thanks for being the USA’s first comet probe back when the powers-that-be did not want to spend the relatively paltry funds to make a probe aimed at Comet Halley, something which the ESA, USSR, and Japan did find the funds and will to accomplish (the USSR even did it as part of a double Venus lander mission! Humanity’s last to date, sadly). You were not even originally meant to study comets when launched in 1978, yet you were able to be redirected to Comet Giacobini-Zinner in 1985, including a flyby boost from Luna.

Now just shove off into deep space mourned only by a few space nerds, your decades of comet and interplanetary data can disappear with you. Maybe some day if we expand into the Sol system you will be recovered, hopefully for your data and role as a true pioneer of the early Space Age and not as a means to make a few fast bucks (or whatever currency will exist by then) for a few individuals.

For those who might think or say that we humans have bigger priorities than recovering an antique comet probe – that is the exactly the problem.

If NASA wants to redeem itself at least a bit in the eyes of many, they will make a DSN dish available to command ICE for one last space mission.

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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